The application of Umberto Scata et al Ser. No. 87,395 filed Oct. 22, 1979 and now abandoned, (and refiled under Rule 60 on Feb. 26, 1981; being now Ser. No. 238,647), describes catalysts for polymerizing alpha-olefins prepared by reacting a Ti compound and an electron-donor compound not containing active hydrogen atoms with a carrier based on Mg dihalide in the form of a complex with electron-donor compounds containing active hydrogen atoms, the Mg dihalide being obtained by decomposition of an organometallic Mg compound, containing at least one R or OR group bound to the Mg atom, wherein R is an alkyl, aryl, cycloalkyl or alkenyl radical having 1 to 20 C. In said Mg compound the remaining valence is saturated by a halogen, a radical R, OR or COX' in which R has the meaning already specified and X' is a halogen.
The catalysts obtained from such catalytic components have improved characteristics with respect to the catalysts obtained by decomposition of the above-mentioned organometallic Mg compounds prior to this invention.
Published British patent application No. 2,014,164 A describes catalysts for polymerizing olefins, consisting of the reaction product of Al-alkyls with a solid catalytic component prepared by reacting a Ti compound and an electron-donor compound with a carrier based on Mg dihalide obtained by decomposition with halogenating agents other than Ti compounds, of the reaction product (d) between an organometallic Mg compound and a hydropolysiloxane compound.
The activity of the catalysts obtained is acceptable only if the decomposition of reaction product (d) is effected in the presence of an aromatic hydrocarbon solvent such as, for example, toluene, xylene, benzene, capable of dissolving reaction product (d) and operating at temperatures not higher than 85.degree. C.